This invention relates to improved hydraulic cement compositions. More particularly, this invention pertains to cement compositions such as Portland cement concretes, mortars, etc., having significantly enhanced compressive strengths due to the incorporation therein of a relatively very small proportion of certain synthetic surface active agents.
Among the various materials added to hydraulic cement compositions such as Portland cement concretes are those which have been found able to affect the interaction between the water and the cement particles in the composition. For instance chemical additives have been used for some time which act to render the wet hydraulic mix more "plastic" at a given proportion of water to cement in the hydraulic mix, or conversely to allow less water to be used in the mix to obtain a given plasticity. These materials are referred to as "dispersing" agents in some cases or as "water reducing" agents in others, although in many instances both terms can be applied to the same additive material.
The ability of a chemical additive to reduce the amount of mix water required to obtain a given plasticity, or "slump" as it is referred to in the art, has led to the valuable utility of the material as a compressive strength-enhancing additive for hydraulic cements. It is well established that other factors being equal, a reduction in the amount of the water employed relative to the cement in the mix (the w/c ratio) will lead to an increase in the extended compressive strength of the hydrated cement compositions as usually measured after 28 days from the preparation of the cement mixture. Among the various chemical materials which have been employed as strength-enhancing, water-reducing agents are carbohydrates; such as saccharides and polysaccharides, for example, starch and derivatives thereof such as pregelatinized starch, dextrin, corn syrup, etc.; polyhydroxy polycarboxylic compounds such as tartaric acid and mucic acid; lignosulfonic acid and salts thereof, for example, sodium lignosulfonate; water soluble borates and silicones; etc., as well as mixtures of the foregoing. These substances are effective as water reducing, strength enhancing additives since they produce no side effects deleterious to strength, although many of these materials will also act to retard the setting time of the hydraulic cement mixture. These materials therefore are normally used in conjunction with a set accelerator such as calcium chloride or a formate salt to offset the retardation effect in instances where such retardation is not also a desired effect.
A chemical agent which has the ability to reduce surface tension in water might be expected to increase the plasticity of wet hydraulic cement mixes by entraining air in the wet mix and indeed the art has long recognized this utility of so-called surface active agents or surfactants. The increased air entrained during mixing due to the presence of the surfactant is normally retained in the final hydrated product, and thus another wide use for surface active materials in the hydraulic cement art has been as air-entraining agents for the hydrated cement product to render it more durable and resistant to freeze-thaw cycles. The amounts of air entrained for these purposes are however deleterious to the compressive strength of the final set product.